configs/beagleboneai64_defconfig: bump Linux to 6.12.70 and U-Boot to 2026.01

This commit:
- updates the Kernel from LTS 6.6.30 to 6.12.70
- updates U-Boot from 2024.04 to 2026.01
- updates arm-trusted-firmware from v2.10 to v2.12 LTS
- switches to Bootlin external glibc stable toolchain

Note: Using the kernel 6.18.9, the SD card fail at boot:

  mmc1: SDHCI controller on 4fb0000.mmc [4fb0000.mmc] using ADMA 64-bit
  Waiting for root device /dev/mmcblk1p2...
  mmc1: error -110 whilst initialising SD card

So let's use stable kernel 6.12.y for the time being.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
[Julien: update linux.hash comment to use upstream hash]
Signed-off-by: Julien Olivain <ju.o@free.fr>

board/beagleboard/beagleboneai64/patches/linux/linux.hash

@@ -1,2 +1,2 @@
-# Locally calculated
-sha256  b66a5b863b0f8669448b74ca83bd641a856f164b29956e539bbcb5fdeeab9cc6  linux-6.6.30.tar.xz
+# From https://www.kernel.org/pub/linux/kernel/v6.x/sha256sums.asc
+sha256  9b4ccec7d8ceff4824f149e476ec06e83c86546ae8af82582871647809a62ef0  linux-6.12.70.tar.xz

board/beagleboard/beagleboneai64/patches/ti-k3-r5-loader/ti-k3-r5-loader.hash

@@ -1,2 +1,2 @@
 # Locally calculated
-sha256  18a853fe39fad7ad03a90cc2d4275aeaed6da69735defac3492b80508843dd4a  u-boot-2024.04.tar.bz2
+sha256  b60d5865cefdbc75da8da4156c56c458e00de75a49b80c1a2e58a96e30ad0d54  u-boot-2026.01.tar.bz2

board/beagleboard/beagleboneai64/patches/uboot/uboot.hash

@@ -1,2 +1,2 @@
 # Locally calculated
-sha256  18a853fe39fad7ad03a90cc2d4275aeaed6da69735defac3492b80508843dd4a  u-boot-2024.04.tar.bz2
+sha256  b60d5865cefdbc75da8da4156c56c458e00de75a49b80c1a2e58a96e30ad0d54  u-boot-2026.01.tar.bz2